Physical activity, sleep duration, and cognitive ageing
Authors: Wenming Shi
Journal: The Lancet Healthy Longevity (2023)

I read with interest Mikaela Bloomberg and colleagues' Article in The Lancet Healthy Longevity on the joint associations of physical activity and sleep duration with cognitive ageing.1Bloomberg M Brocklebank L Hamer M Steptoe A Joint associations of physical activity and sleep duration with cognitive ageing: longitudinal analysis of an English cohort study.Lancet Healthy Longev. 2023; 4: e345-e353Summary Full Text Full Text PDF Google Scholar Including data from 8958 adults (aged 50–95 years at baseline) in the English Longitudinal Study of Ageing, the findings suggested that both regular physical activity and sufficient sleep are necessary to reduce cognitive decline. However, I have several concerns about the Article. First, a key concern is that the authors might have overlooked two major confounders—sedentary behaviour (eg, sitting) and adverse childhood experiences. Increased sitting time is well known to have become common in modern life due to the popularisation and widespread use of electronic devices, changes in transportation patterns, and an increase in sedentary occupations. A survey of 3086 US adults showed that replacing sedentary activities with moderate-to-vigorous physical activity was associated with better cognition outcomes, particularly among those who slept no longer than 7 h per night.2Wei J Hou R Xie L et al.Sleep, sedentary activity, physical activity, and cognitive function among older adults: the National Health and Nutrition Examination Survey, 2011–2014.J Sci Med Sport. 2021; 24: 189-194Summary Full Text Full Text PDF PubMed Scopus (15) Google Scholar Notably, sedentary behaviour might partly diminish the benefits of physical activity during the rest of the day. To strengthen the findings of Bloomberg and colleagues, taking sedentary behaviour into account in further investigations would be instructive. Adverse childhood experiences might be another important confounder. Evidence has shown that increased exposure to adverse childhood experiences was associated with an increased risk of cognitive decline or dementia in older adults.3Tani Y Fujiwara T Kondo K Association between adverse childhood experiences and dementia in older Japanese adults.JAMA Netw Open. 2020; 3e1920740 Crossref Scopus (48) Google Scholar In a nationally representative study of 22 403 US adults, higher numbers of adverse childhood experiences increased the risk of chronic short sleep duration duration (<6 h per night), and the association held for all decades of age until participants reached their 60s.4Sullivan K Rochani H Huang LT Donley DK Zhang J Adverse childhood experiences affect sleep duration for up to 50 years later.Sleep. 2019; 42: 1-9Crossref Scopus (0) Google Scholar Such factors should be taken into consideration in the discussion of the findings by Bloomberg and colleagues. Second, I noticed that information on APOE genotype was not available in this study. APOE ε4 carrier status might be linked to an increased rate of cognitive decline later in life. According to a prospective cohort study, better sleep consolidation might attenuate the effect of the APOE ε4 allele on incident Alzheimer's disease in older adults.5Lim AS Yu L Kowgier M Schneider JA Buchman AS Bennett DA Modification of the relationship of the apolipoprotein E ε4 allele to the risk of Alzheimer disease and neurofibrillary tangle density by sleep.JAMA Neurol. 2013; 70: 1544-1551Crossref PubMed Scopus (192) Google Scholar Considering this factor, when assessing the associations of physical activity and sleep duration with cognitive ageing, examining effect modifications by APOE genotype in further studies might be meaningful. I declare no competing interests.